In the automatic testing of integrated circuits (IC) and other electronic devices, special device handlers have been used which bring the device to the proper temperature and places the device to be tested in position. The electronic testing itself is provided by a large and expensive automatic testing system which includes a test head which has been required to connect to and dock with the device handler. The Device Under Test (DUT) requires precision, high speed signals for effective testing; accordingly, the electronic circuits must be located as close as possible to the DUT. This causes the test head to be extremely heavy.
Test head positioner systems may be used to position the test head with respect to the device handler. When the test bead is accurately in position with respect to the device handler, the test head and the device handler are said to be aligned. When the test head and device handler are aligned, the fragile test head and device handler electrical connectors can be brought together (i.e., docked), enabling the transfer of test signals between the test head and the device handler. Prior to docking, the fragile test head and device handler electrical connectors must be precisely aligned to avoid damaging the fragile electrical connectors.
A test head positioner system may also be referred to as a test head positioner or a test head manipulator. This technology is described, for example, in the inTEST Handbook, inTEST Corporation. This technology is also described, for example, in U.S. Pat. Nos. 5,608,334, 5,450,766, 5,030,869, 4,893,074 and 4,715,574 which are all incorporated by reference for their teachings in the field of test head positioner systems.
For purposes of this explanation, a device under test (DUT) is the present device (IC) undergoing test. A test station apparatus (TSA) refers collectively to wafer probers, device handlers and manual test stations.
To be consistent with descriptions of test head positioner systems in the prior art, the coordinate system 100 illustrated in FIG. 1 is used in which:                Y=vertical, up-down axis 102        X=horizontal, side-to-side or left-right axis 104        Z=horizontal, in-out axis 106.        
When viewed from the front of the manipulator, this forms the Cartesian coordinate system.
Rotations about the axes are designated as follows:                Theta Y=rotation about the Y axis (hereinafter referred to as “swing”) 108        Theta Z=rotation about in-out axis (hereafter referred to as “roll” or “twist”) 110        Theta X=rotation about X axis (hereinafter referred to as “tumble” or “pitch”) 112        
A reference model for a test floor 200 is shown in plan view in FIG. 2. As shown, Main Test Equipment Cabinet (Tester Cabinet) 202, a TSA 204, a manipulator 206, and a test head 208 are included.
FIG. 3 shows a rectangular box-shaped test head 300 oriented such that its top 302 and bottom 304 surfaces are parallel with the X-Z plane, the sides 308 are parallel with the Y-Z plane, and the front and rear 306 are parallel with the X-Y plane.
The test head includes a test interface on one surface. The test interface typically holds a test interface board, which in addition to other functions, provides connection points to the test apparatus in the prober, handler, or manual test station. The surface having the test interface is hereinafter called the “interface surface” (IS) 310. The IS defines both a plane and a direction; the direction is described by a vector normal to the IS plane and pointing away from the test head. FIG. 3 shows the IS 310 in the horizontal plane with upwards direction. In use, the orientation of the test head will change as it is docked with different types of equipment. Accordingly, both the plane and the direction of the IS 310 will also change.
It is helpful to designate test head dimensions with respect to the interface surface. With the orientation shown in FIG. 3 (IS facing up), the following definitions may be used:                T=test head thickness=dimension in the up-down direction 312.        W=test head width=dimension in the side-to-side direction 314.        L=test head length=dimension in the in-out direction 316.        
In use, the test head may be brought upwards to contact the DUT as in a device handler. In this case, the interface surface is facing up (IS UP).
Another alternative is that the test head may be brought downwards to contact the device as in a prober. In this case, the interface surface is facing down (IS DOWN).
Thirdly, both the DUT and the IS may be orientated in a vertical plane (IS vertical).
Fourthly, both the DUT and the IS may be oriented at any angle between the IS up and IS down.
As the test head is moved from one apparatus to another, it is clear that the test head must be rotated among IS UP, IS DOWN, and IS Vertical positions. Depending upon the manipulator, this may be effected by rotation in either the tumble (pitch) or roll (twist) coordinates.
The test head is connected to the test cabinet by a large, thick bundle of cables. The cables, size, weight and resistance to flexing and twisting all interfere with and constrain test head motion. Test head motion is desirably performed in a manner to protect the cable from several factors as described, for example in U.S. Pat. No. 5,608,334.
Many test heads, particularly large ones, are attached to the manipulator using a “cable-pivot” apparatus. In the cable-pivot mode, the cable is brought from the test head at the center of rotation and parallel with the axis of rotation (normally the roll or twist axis). This is described, for example, in U.S. Pat. Nos. 5,030,869, 5,450,766 and 5,608,334.
It is desirable to support the cable in a manner to minimize interference with test head motion. It is also desirable to protect the cable from stress. For this purpose, a telescopic cable support mechanism 400, as shown in FIG. 4, may be used. Such a mechanism is described, for example, in U.S. Pat. No. 4,893,074.
Referring to FIG. 5A, a conventional test head positioner system 500 is shown.
Test head positioner system 500, may include, for example, main arm 511 and projected cradle assembly 520 which is described in U.S. Pat. No. 5,450,766.
As shown in FIG. 5, the main arm 511 is coupled to linear guide rail 510. Main arm 511 moves vertically in either direction along linear guide rail 510. A lock mechanism (not shown) allows the position of main arm 511 to be fixed relative to linear guide rail 510. Positioner assembly 501 is adapted to ride vertically on linear guide rail 510 by a counter weight assembly (not shown) which moves vertically in either direction within the rear section of column 545. The counter weight assembly enables the test head to be moved vertically with minimal force. In addition, the test head is mounted according to its center of gravity. Cables 512 extend from test cabinet 514 and into the rear section of test head 502.
Cradle assembly 520 is coupled to main arm 511. Cradle assembly 520 has a front “C” shaped section which is coupled to test head 502, such that test head 502 may pitch about an axis passing through its center of gravity. Operation and details regarding cradle assembly 520 are fully explained in U.S. Pat. No. 5,450,766 and are not repeated here.
Column 545 rests upon translation table 521. Translation table includes side-to-side plate 522, in-out plate 524, turntable 526 and base 530. Column 545 is coupled to side-to-side plate 522. Guides 523 in side-to-side plate 522 and the rails (not shown) of in-out plate 524 couple side-to-side plate 522 to in-out plate 524. Guides 525 of in-out plate 524 are coupled to the rails 527 of turntable 526. Turntable 526 is, in turn, coupled to base 530 with a bearing surface (not shown). Column 545 may be repositioned as desired along the x and z-axes by moving side-to-side table 522 and in-out table 524, respectively. Column 545 may also be rotated about the y-axis by rotating turntable 526 about its coupling with base 530. Of course, as column 545 is moved along these axes, test head 502 is repositioned.
FIG. 5B is similar to FIG. 5A except for the relative positions of the parts associated with translation table 521. In particular, the turntable 526 is between column 545 and side-to-side plate 522. In addition, guides 525 of in-out plate 524 are directly coupled to base 530 at rails 531. In all other aspects, FIGS. 5A and 5B are similar. Therefore, the remaining details of FIG. 5B are not repeated here.
Other combinations of horizontal motions built into the manipulator base are possible. If such motions are not built into the base, they are typically provided in the arm assembly. For example the inTEST Corp. in2 manipulator first described in U.S. Pat. No. 4,527,942 provides no horizontal motions in its base; an articulating arm assembly provides all horizontal motion. Further, manipulators are known which have bases that provide only swing rotation motion, such as the system described in U.S. Pat. No. 5,606,262, assigned to Teradyne.
Several manipulators provide two motions in their bases. A manipulator manufactured by Teradyne and described in U.S. Pat. Nos. 5,931,048 and 5,5,949,002 provides swing rotation and side-to-side motion in its base with the swing mechanism at the bottom; in-out motion in this manipulator is provided in the arm and cradle assemblies. A further manipulator manufactured by Reid-Ashman MFG, Inc., provides side-to-side and in-out motion in the base with swing provided by rotation the arm about a shaft attached to the column.
A manipulator manufactured by Schulmberger provides side-to-side motion and swing rotation motion in its base with the swing mechanism on top of the side-to-side mechanism. In-out and roll motions are provided in the arm assembly. This manipulator is unique in that the cable passes from the cabinet, through the center of the column above the center of rotation, to terminate at the test head. Also unique to this manipulator is a spring mechanism that serves as a counter balance which was first described in U.S. Pat. Nos. 4,943,020 and 4,973,015, both assigned to Schulmberger.
Finally, a further manipulator, also manufactured by Reid-Ashman MFG, Inc., provides all three motions in its base with the swing rotation mechanism at the bottom.
In operation, the test head 502 is manipulated towards the docking position, using in part the translation table described above. When the test head is within a distance of 1 cm to 2 cm to its ultimate docked position, an alignment apparatus starts to engage. At this point, a docking actuator is engaged which draws the test head into the final aligned test position and into engagement with the DUT test fixture and/or probe card. As the test head is drawn into position, the alignment apparatus, such as tapered pins engaging mating holes, reduces any initial error to within a small allowable tolerance. During dock actuation, the test head is desirably free to move in any combination of axes and rotations to assure final alignment and parallelization. Thus, all axes should be free during dock actuation.
Similarly, when undocking, all axes should be free as the dock actuation process is reversed. Now the dock mechanism pushes the test head away from engagement with the test socket/probing assembly apparatus. Once undocked, selected axes can be secured, if so desired, to allow the test head to be moved away from the prober/handler, using only one motion axis.
Recent advances in the semiconductor industry have had the following effects:                1. DUTs have become more complex; the number of transistors per device has grown steadily from a few thousand to a few million.        2. DUTs have become increasingly complex mixtures of digital circuitry, analog circuitry, and mixed signal circuitry.        3. The number of I/O, power supply and signal ground reference pins per device has grown to several hundreds from less than one hundred.        4. DUT clock rates have gone from 10's of MHz to at least 1 GHz.        5. Data, Address and Control signals are accordingly in at least the 100's of Mbps range.        6. Per pin frequency bandwidth requirements are at least in the 10's of GHz range.        
As a result, the following test system design changes have become desirable:                1. More, faster and more complex pin-electronics circuits in the test head.        2. Greater power dissipation per pin circuit in the test head can be expected due to the higher switching rates.        3. Water cooling systems with circulating water have been added to the test heads, increasing their weight and necessitating flexible plumbing to be included in the test head cable.        4. More power supply and ground conductors of heavier gauges are in the interconnecting test head cable.        5. Moving circuitry from the system cabinet to the test head to reduce the amount of signal wiring and associated delays in the cable.        
These factors have driven the size and weight of test heads to increase significantly while at the same time requiring:                1. The demand that the test head be brought into close proximity to the DUT is increasingly important.        2. The cable from test head to tester cabinet be kept as short as possible while at the same time it has become thicker and stiffer.        
Thus, test heads and their associated cables have become significantly larger and heavier.